An analytical apparatus utilizing the principle of immunochromatography (hereinafter referred to “as immunochromatography apparatus”) is known in the art, as mentioned below. Thus, it comprises:                a protective case containing a sheet-like developing member or element through which a sample liquid can be developed owing to the capillary phenomenon and/or diffusion;        an application zone, disposed at one end of the developing member, for applying the sample liquid containing an analyte;        an water-absorbing zone, disposed at the other end of the developing member, for receiving the liquid that has moved through the developing member owing to the capillary phenomenon;        a sealed-in zone disposed therebetween at a site closer to the application zone and containing a substance labeled with a substance having a binding affinity for the analyte (an analyte-binding labeled substance):        a detection zone disposed at a site remoter from the application zone fixed with a substance capable of binding to the analyte, which has a binding affinity for the analyte, but has no same binding affinity as that of the analyte-binding labeled substance, to bind the complex resulting from binding of the analyte to the analyte-binding labeled substance; and        an observation window formed in the protective case so that the detection zone can be observed.        
The “analyte” includes DNAs, RNAs, immunochemically active substances and glycoproteins. The “substance capable of binding to the analyte” includes DNAs, RNAs, immunochemically active substances and lectins. The “label substance” includes metal colloids, dyes, latices, fluorescent substances and enzymes. The “analyte-binding labeled substance” includes DNAs, RNAs, oligonucleotides, biotin, avidins, streptavidin and digoxigenin.
In the analytical procedure using such an immunochromatography apparatus, a sample liquid containing an analyte to be detected or assayed is first applied to the application zone. The sample liquid moves to the sealed-in zone containing an analyte-binding labeled substance owing to the capillary phenomenon. In the sealed-in zone, the analyte-binding labeled substance binds to the analyte through an affinity (for example, immunological affinity) therebetween to give a labeled complex. The labeled complex is developed and migrates through the developing member to the detection zone owing to the capillary phenomenon and/or diffusion and captured by the substance having an affinity therefor as immobilized in the detection zone. The label, or marker, of the labeled complex captured in the detection zone is measured or detected by visual observation or by some other means through the observation window of the protective case, whereby the analyte contained in the sample liquid can be quantitated or judged for the presence or absence thereof.
Another immunochromatography apparatus, such as mentioned below, is also known. Thus, a sheet-like developing member through which a sample liquid can be developed owing to the capillary phenomenon and/or diffusion is contained in a protective case, one end of the developing member is provided with an application zone for applying an analyte-containing sample liquid, and the other end is provided with an absorption zone for receiving the liquid that has migrated through the developing member owing to the capillary phenomenon. Between the zones, there is disposed, at a site closer to the application zone, a sealed-in zone containing a substance labeled with a substance having a binding affinity for the analyte and a substance resulting from coupling of a binding substance differing from the above-mentioned analyte-binding substance but having a binding affinity for the analyte with a binding label substance differing from the above-mentioned label substance. On the side remoter from the application zone, there is disposed a detection zone with a substance immobilized therein and capable of binding to the above binding label substance to thereby bind to a complex composed of the analyte, the analyte-binding substance-labeled substance and the analyte-binding substance coupled with the above binding label substance. The protective case of the immunochromatography apparatus is provided with an observation window so that the detection zone can be observed. For knowing the result of the analysis using this immunochromatography apparatus, too, the label captured in the detection zone is measured or detected through the observation window of the protective case by visual observation or by some other means, whereby the analyte contained in the sample liquid can be quantitated or judged for the presence or absence thereof.
This immunochromatography apparatus is characterized in that the reagents contained in the apparatus are maintained in a dry state during storage before use, hence can be stored at room temperature for a prolonged period of time. Analyses using such immunochromatography apparatus make it possible for a doctor or medical practitioner himself or herself to immediately test a sample collected by him or her, so that the doctor can make a diagnosis comprehensively in a short time based on the clinical symptoms of a patient and the immunological test results. Thus, advantageously, the timing of treatment will scarcely be lost.
As regards the housing for such immunochromatography apparatus, the following technologies are known in the art.
Japanese Patent Application No. 2705768 teaches that a strip or sheet comprising a dry porous immunochromatographic carrier material should be contained in a hollow housing having an opening for detection. The strip or sheet is backed with a transparent sheet made of a plastic material or sandwiched between two plastic material sheets, at least one of which is transparent, and disposed adjacent to the opening so that moisture or the sample liquid can be prevented from entering the housing inside through the opening. According to the above patent, the housing material is opaque or semitransparent and at least one of the plastic sheet materials is transparent.
Japanese Patent Application No. 2825349 teaches that a sample liquid should be taken from one end of an absorbent member for accommodating sample and caused to move to the place of an absorbent member for accommodating sample covered by a housing and the analyte in the sample be observed through a reading window provided on the housing and that the observation window of the housing should be covered with a cap during sample taking and, after sample taking, the cap be removed and placed on the sample taking side.
As for the technology of displaying a detection line in the observation window of an immunochromatography apparatus, the prior art includes the following.
In JP-A No. 230009/1994, an immunoassay tool is shown in which an indicator capable of changing its color upon passage of a liquid sample and retaining the changed color for a long period of time is immobilized in a judging/displaying part to thereby cause the site of immobilization to retain the indicator for a long period of time and by which whether the test liquid has passed the observation window or, in other words, whether the judgment has become possible, can be established.
JP-A No. 145712/1997 discloses an immunochromatography apparatus in which the upper surface of an immunochromatographic material having a water-insoluble colored material immobilized thereon is covered with a water-soluble, optically opaque substance so that whether a solution applied to the chromatography apparatus has passed the measurement area can be displayed to thereby indicate that the apparatus is now in a condition ready for judgment and in which the condition ready for judgment is thus indicated by dissolution of the covering substance.
It is a problem with the prior art immunochromatography apparatus that when the concentration of a substance to be detected is low, the substance cannot be detected or different testers may give different judgment results although when the concentration of the test substance in the sample solution is not lower than a certain level, the substance can be detected through the observation window.
In the prior art immunochromatography apparatus, the housing containing a developing strip is opaque or semitransparent, so that when a sample solution is developed through a developing strip, how far the development has advanced can be confirmed only through the observation window or a confirmation window for confirming the extent of development of the sample solution. If the sample solution is a viscous liquid, the liquid may stop penetrating in the middle of the strip or may be too late getting to the detection site. If the liquid fails to arrive at the detection site within a predetermined period of time, the test, which is in reality positive, may possibly be judged negative.
In the prior art chromatography apparatus, the developing strip is exposed in the window or, even when the developing strip is covered with a transparent sheet, the window is not in a completely closed condition, so that the sample solution or the like may be splashed on the window by mistake or without being noticed or the sample solution or the like may further enter the inside, contaminating the developing strip or causing an erroneous diagnosis.